At the time, it was one of the greatest air tragedies in American flight history. In 1955, 66 people were killed when their jet airliner crashed into a mountain side in Wyoming. Video shows that debris from that crash still remain.

It was United Airlines Flight 409. To be specific, it really wasn't a "jet airliner" as we think of it today. It was a Douglas DC-4 which was a 4-propeller driven airliner as Wikipedia documents. On October 6, 1955, it was scheduled to fly from New York City to San Francisco with stops in Denver and Salt Lake City. It never arrived in Salt Lake City. Here's part of how Wikipedia remembers that awful day:

Flight 409 left New York, New York one hour and 11 minutes late. Routine crew changes were made in Chicago and Denver. Flight 409 departed Denver, Colorado at 6:33 a.m. on October 6, 1955, 83 minutes after its scheduled departure time. The assigned path the airliner was expected to fly was along airways V-4 Denver to Laramie, Wyoming V-118 to Rock River, Wyoming radio, V-6 to Fort Bridger, Wyoming, and V-32 to a landing in Salt Lake City.

When a radio check-in in Rock Springs didn't happen as scheduled, the airliner was reported missing. The Wikipedia page mentions that there was no active radar in use in that area in 1955 so they had to search visually for the plane. The Wyoming Air National Guard eventually found the remains of the plane, remnants of which are still visible to this day near Medicine Bow Peak.

66 lives were lost that day and the crash of United Airlines Flight 409 led to improved safety checks of planes and better radar coverage of that part of Wyoming. As the adventurer showed in his video, a simple memorial marks the spot of this great tragedy in Wyoming history.

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